1. Field of the Invention
The present invention relates to a magentic recording material and, more particularly, to a magnetic recording material which enables a large amount of information to be recorded in a small area of recording, and which has excellent sliding properties and durability.
2. Description of the Prior Art
Magnetic recording materials, particularly video tapes, must have a small coefficient of friction and ensure smooth and stable tape-running for a long time since they run in contact with a fixed head, drums, guide poles or the like. In addition, they must possess excellent durability since they are vigorously rubbed with a rotary magnetic head.
Therefore, incorporation of higher fatty acids, higher fatty acid esters, paraffin hydrocarbons, silicone oils (e.g., dimethylpolysiloxane, diphenylpolysiloxane, etc.), or the like in a magnetic coating containing a ferromagnetic powder and a binder has been previously employed. In particular, silicone oils have often been employed since good effects are obtained even when a small amount of silicone oil is used.
These additives discussed above are described in Japanese Patent Publication Nos. 18064/66, 186,68, 669/68, 15624/72, U.S. Patents 2,654,681, 3,470,021, 3,497,411, 3,525,694, 3,634,253, etc.
However, sufficient sliding property and durability required for video tapes have not been achieved with these conventional additives. In addition, a so-called blooming phenomenon of these additives oozing out on the surface of a magnetizable layer has tended to occur, which leads to sticking of tapes upon storage.
Organic silicone compounds represented by the following general formula [II] (as described in Japanese Patent Publication No. 14249/74) ##STR2## wherein R and R' each represents a hydrocarbyl group having 7 to 26 carbon atoms, and n represents an integer of 1 to 20; and the following general formula [III] (as described in Japanese Patent Application (OPI) No. 32904/75). ##STR3## wherein R and R' each represents a hydrocarbyl group having 8 to 18 carbon atoms, R" represents a hydrogen atom or a methyl group, 15.gtoreq.m.gtoreq.1, and 16.gtoreq.(n.sub.1 +n.sub.2).gtoreq.2; are also known.
However, durability is not improved with the compounds represented by the above general formula [II] and, in addition, these compounds have such a low compatibility with a binder that they cause the blooming phenomenon, which is disadvantageous, to occur. The reason for this may be the bond between the hydrocarbyl group and silicon atom is an ether bond and such has a low degree of polarity, although this is not certain.
Also, the compounds represented by the above general formula [III] have been found to be disadvantageous since they exhibit such a high kinetic coefficient of friction with a head drum of video tape recorders upon high load being applied that squeaking with the drum sometimes occurs. In addition, durability is not improved very much with these compound. This may be attributed to the hydrophilic alkyleneoxide chain in the molecule, although again this is not certain.